Keratinocyte growth factor (KGF) belongs to the family of fibroblast growth factors (“FGFs”), the prototypes of which are represented by basic FGF and acidic FGF. KGF is also known as FGF-7. KGF, like FGFs, binds heparin and is generally capable of stimulating the proliferation and differentiation of a variety of cell types derived from the primary or secondary mesoderm as well as from neuroectoderm. For example, KGF, like FGFs, has the ability to induce the differentiation and proliferation of ventral as well as dorsal mesoderm in early blastulae. See, e.g., Gospodarowicz et. al. Cell. Biol. Rev. (1991) 25:307-314; and Basilico et al. Adv. Cancer Res. (1992) 59:115-165.
Like other FGFs, KGF is a heparin-binding protein, but unlike other FGFs, it has a unique target cell specificity. Particularly, KGF is similar to other FGFs in its ability to stimulate epithelial cell proliferation, but is dissimilar to other FGFs in its inability to stimulate endothelial cells or fibroblast proliferation. See, e.g., Finch, et. al. Science (1989) 245: 752-755. Mature, full-length KGF, designated herein as KGF163, is a polypeptide with 163 amino acid residues, and possesses a potential N-glycosylation site that extends from amino acid residue 14 to 16 at the N-terminus. Finch, et. al. Science (1989) 245: 752-755.
Ron et al. J. Biol. Chem. (1993) 268:2984-2988 found that when KGF163 was expressed in a prokaryotic expression system, a recombinant KGF (“rKGF”) polypeptide could be obtained that possessed mitogenic activity. When the rKGF molecule was truncated by deletion of 3, 8, 27, 38, and 48 amino acid residues from the N-terminus of the mature KGF163 polypeptide, biological activity of the resulting molecules varied. With deletion of 3 and 8 amino acid residues, respectively, the mitogenic activity of the resulting molecules did not appear to be affected as compared to full-length rKGF. Deletion of 27 amino acid residues, however, resulted in molecules that displayed 10-20 fold reduced mitogenic activity. Deletion of 38 and 48 amino acid residues, respectively, resulted in complete loss of mitogenic activity and heparin-binding ability. Ron et al., however, failed to produce any truncated rKGF fragments that possessed increased mitogenic activity as compared to the full-length rKGF molecule.
U.S. Pat. Nos. 5,677,278, 5,773,586, 5,843,883, 5,863,767 and 6,074,848, all to Gospodarowicz et al., describe KGF molecules. One particular molecule, with an N-terminal deletion of 23 amino acid residues, termed KGFdes1-23, demonstrates enhanced mitogenic activity as compared to mature, full-length recombinant KGF163.
Osslund et al. Protein Sci. (1998) 7:1681-1690 reports various N-terminal truncated KGF molecules and certain measurements of their mitogenic activity. Similarly, International Publications WO 96/11951 and WO 96/11949 describe KGF molecules with various N-terminal truncations and amino acid substitutions.